This invention relates generally to an electrophotographic printing machine, and more particularly concerns a cleaning system employed therein.
In the process of electrophotographic printing, for example, as disclosed in U.S. Pat. No. 2,297,691 issued to Carlson in 1942, a photoconductive member is charged to a substantially uniform level. The light image of an original document being reproduced is projected onto the charged photoconductive member selectively dissipating the charge thereon. This records a latent image of the original document on the photoconductive member. Thereafter, a developer mixture of carrier granules and toner particles is brought into contact with the latent image. The latent image electrostatically attracts the toner particles from the carrier granules in image configuration. The developed toner powder image is then transferred to a sheet of support material such as paper, and permanently affixed thereto to form a permanent copy of the original document.
During the transfer step, substantially all of the toner particles are caused to adhere to the sheet of support material forming the informational areas thereon. However, a small portion of the toner particles frequently remain on the photoconductive member. This small quantity of toner particles remaining on the photoconductive member will affect subsequent operation of the electrophotographic process. If these toner particles remain thereon, they will have a cumulative affect in that additional residual toner particles will adhere more readily to the photoconductive member in both the image and non-image area thereof.
Typically, a rotating brush in peripherial contact with the surface of the photoconductive member is employed to clean residual toner particles adhering thereto. The brush, in turn, may be cleaned by a flicker bar and by a vacuum system similar in structure to the common household vacuum cleaner. The residual toner particles are entrained in the air and then removed therefrom by a suitable filter in the cleaning system.
One disadvantage that a system of this has type is high air flows must be maintained to keep that the residual toner particles airborne. This has necessarily led to a large and complicated vacuum system increasing the cost and decreasing the reliability of the electrophotographic printing machine. More particularly, the blower requires excessive power to develop the high air velocities required to maintain the toner particles airborne. If a high air velocity is not maintained, the toner particles will settle to the bottom of the tubing and will not be removed from the printing machine. This imposes the requirement of a large air moving system to advance these fine toner particles. Systems of this type are extremely noisey and consume excessive power. Thus, it would be extremely advantageous to be able to develop a low velocity air cleaning system.
Accordingly, it is a primary object of the present invention to improve the cleaning system employed in an electrophotographic printing machine.